WASHINGTON ACADEMY OF SCIENCES 75 



the relation of these slopes to the subjacent surface of earth and rock; and 

 all this without a single glacial stria or an inch of ice-polish, save in one 

 small spot, in the whole tract of 16,500 square miles. It is necessary 

 to conceive not only the mode of melting of the ice at each league of its 

 retreat, but also every considerable brook, every river, and every lake or 

 pond formed by the melting, both at its under surface and on its upper sur- 

 face; it is necessary to restore not only the margin of the mer de glace under 

 each minute of latitude it occupied, but, as well, the canyons by which it 

 was cleft, the floe-bearing lakes and mud-charged marshes with which it 

 was fringed, each island of ice, and each ice-bound lake formed within its 

 limits. And it is not only necessary to reconstruct the geography of a 

 dozen episodes, as does the anatomist the skeleton from a few bones, but 

 to develop a geography such as civilized eye has never seen, and which 

 could only exist under conditions such as utterly transcend the experience 

 of civilized man. All this has been done. The trail of the ice monster 

 has been traced, his magnitude measured, his form and even his features 

 figured forth, and all from the slime of his body alone, where even his 

 characteristic tracks fail. 



This now somewhat famous geologic section is situated on the 

 crest of Capitol Hill, at the south end of the Capitol grounds, in Des 

 Moines, Iowa. As originally described in the American Journal of 

 Science (Vol. xxiv, p. 202, 1882,) the exposure of deposits presents the 

 following relations: 



5. Till, light reddish buff clay with pebbles (feet) 7 



4. Till, contorted and interstratified with loess 5 



3. Loess, with numerous fossils 15 



2. Till, dark red clay with abundant pebbles 6 



1. Shale (Carboniferous) exposed 10 



Three important features are especially to be noted: (1) The lower 

 till (No. 2) represents what is now called the Kansas drift, which 

 was formed when the great continental glacier, reaching southward to 

 St. Louis and Kansas City, attained its greatest extent and thickness; 

 (2) the loess members composed of fine loams (Nos. 3 and 4) consti- 

 tuted the soil formation during a long interglacial epoch when the 

 climate was not very different from what it is at the present day; 

 and (3) the upper till (No. 5) represents what is now known as the 

 Wisconsin drift. 



